Thermus caldifontis sp. nov., a thermophilic bacterium isolated from a hot spring.

A thermophilic bacterial strain, designated YIM 73026T was isolated from a sediment sample collected from a hot spring in Tibet, PR China. The taxonomic position of the novel isolate was investigated by a polyphasic approach. The novel isolate was Gram-stain-negative, aerobic and rod-shaped. Colonies were circular, convex, opaque and yellow. The strain grew at 50-70 °C (optimum, 60 °C), pH 6.0-8.0 (optimum, pH 7.0) and in the presence of up to 1.0 % NaCl (w/v). Comparison of the 16S rRNA gene sequences of YIM 73026T and those of other members of the genus Thermus showed sequence similarities ranging from 91.2 to 97.5 %, with YIM 73026T showing closest sequence similarity to Thermus scotoductus SE-1T (97.5 %). DNA-DNA hybridization results, however, revealed that DNA-DNA reassociation values between YIM 73026T and T. scotoductus DSM 8553T (37.6 %), Thermusamyloliquefaciens YIM 77409T (34.5 %), Thermusantranikianii DSM 12462T (30.3 %), Thermuscaliditerrae YIM 77925T (28.6 %) and Thermustengchongensis YIM 77924T (27.3 %) were well below the 70 % limit for species identification. YIM 73026T contained MK-8 as the respiratory quinone, and iso-C15 : 0, iso-C16 : 0, iso-C17 : 0 and anteiso-C15 : 0 as the major cellular fatty acids (>10 %). The polar lipids consisted of one aminophospholipid, one phospholipid and two glycolipids. The genomic DNA G+C content of YIM 73026T was 65.4 mol%. On the basis of morphological, chemotaxonomic and genotypic characteristics, it is proposed that the isolate represents a novel species of the genus Thermus, for which the name Thermus caldifontis sp. nov. is proposed. The type strain is YIM 73026T (=NBRC 112415T=CCTCC AB 2016305T).